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dm snapshot: track snapshot reads
Whenever a snapshot read gets mapped through to the origin, track it in a per-snapshot hash table indexed by chunk number, using memory allocated from a new per-snapshot mempool. We need to track these reads to avoid race conditions which will be fixed by patches that follow. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mikulas Patocka
Alasdair G Kergon
parent
def052d21c
commit
cd45daffd1
@ -40,6 +40,11 @@
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*/
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#define SNAPSHOT_PAGES (((1UL << 20) >> PAGE_SHIFT) ? : 1)
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/*
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* The size of the mempool used to track chunks in use.
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*/
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#define MIN_IOS 256
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static struct workqueue_struct *ksnapd;
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static void flush_queued_bios(struct work_struct *work);
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@ -93,6 +98,42 @@ static struct kmem_cache *exception_cache;
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static struct kmem_cache *pending_cache;
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static mempool_t *pending_pool;
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struct dm_snap_tracked_chunk {
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struct hlist_node node;
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chunk_t chunk;
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};
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static struct kmem_cache *tracked_chunk_cache;
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static struct dm_snap_tracked_chunk *track_chunk(struct dm_snapshot *s,
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chunk_t chunk)
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{
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struct dm_snap_tracked_chunk *c = mempool_alloc(s->tracked_chunk_pool,
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GFP_NOIO);
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unsigned long flags;
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c->chunk = chunk;
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spin_lock_irqsave(&s->tracked_chunk_lock, flags);
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hlist_add_head(&c->node,
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&s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)]);
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spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
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return c;
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}
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static void stop_tracking_chunk(struct dm_snapshot *s,
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struct dm_snap_tracked_chunk *c)
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{
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unsigned long flags;
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spin_lock_irqsave(&s->tracked_chunk_lock, flags);
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hlist_del(&c->node);
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spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
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mempool_free(c, s->tracked_chunk_pool);
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}
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/*
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* One of these per registered origin, held in the snapshot_origins hash
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*/
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@ -482,6 +523,7 @@ static int set_chunk_size(struct dm_snapshot *s, const char *chunk_size_arg,
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static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
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{
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struct dm_snapshot *s;
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int i;
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int r = -EINVAL;
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char persistent;
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char *origin_path;
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@ -564,11 +606,24 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
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goto bad5;
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}
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s->tracked_chunk_pool = mempool_create_slab_pool(MIN_IOS,
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tracked_chunk_cache);
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if (!s->tracked_chunk_pool) {
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ti->error = "Could not allocate tracked_chunk mempool for "
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"tracking reads";
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goto bad6;
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}
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for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
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INIT_HLIST_HEAD(&s->tracked_chunk_hash[i]);
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spin_lock_init(&s->tracked_chunk_lock);
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/* Metadata must only be loaded into one table at once */
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r = s->store.read_metadata(&s->store);
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if (r < 0) {
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ti->error = "Failed to read snapshot metadata";
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goto bad6;
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goto bad_load_and_register;
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} else if (r > 0) {
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s->valid = 0;
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DMWARN("Snapshot is marked invalid.");
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@ -582,7 +637,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
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if (register_snapshot(s)) {
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r = -EINVAL;
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ti->error = "Cannot register snapshot origin";
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goto bad6;
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goto bad_load_and_register;
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}
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ti->private = s;
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@ -590,6 +645,9 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
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return 0;
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bad_load_and_register:
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mempool_destroy(s->tracked_chunk_pool);
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bad6:
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dm_kcopyd_client_destroy(s->kcopyd_client);
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@ -624,6 +682,9 @@ static void __free_exceptions(struct dm_snapshot *s)
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static void snapshot_dtr(struct dm_target *ti)
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{
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#ifdef CONFIG_DM_DEBUG
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int i;
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#endif
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struct dm_snapshot *s = ti->private;
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flush_workqueue(ksnapd);
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@ -632,6 +693,13 @@ static void snapshot_dtr(struct dm_target *ti)
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/* After this returns there can be no new kcopyd jobs. */
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unregister_snapshot(s);
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#ifdef CONFIG_DM_DEBUG
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for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
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BUG_ON(!hlist_empty(&s->tracked_chunk_hash[i]));
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#endif
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mempool_destroy(s->tracked_chunk_pool);
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__free_exceptions(s);
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dm_put_device(ti, s->origin);
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@ -974,14 +1042,10 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
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start_copy(pe);
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goto out;
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}
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} else
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/*
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* FIXME: this read path scares me because we
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* always use the origin when we have a pending
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* exception. However I can't think of a
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* situation where this is wrong - ejt.
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*/
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} else {
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bio->bi_bdev = s->origin->bdev;
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map_context->ptr = track_chunk(s, chunk);
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}
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out_unlock:
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up_write(&s->lock);
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@ -989,6 +1053,18 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
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return r;
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}
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static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
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int error, union map_info *map_context)
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{
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struct dm_snapshot *s = ti->private;
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struct dm_snap_tracked_chunk *c = map_context->ptr;
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if (c)
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stop_tracking_chunk(s, c);
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return 0;
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}
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static void snapshot_resume(struct dm_target *ti)
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{
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struct dm_snapshot *s = ti->private;
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@ -1266,6 +1342,7 @@ static struct target_type snapshot_target = {
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.ctr = snapshot_ctr,
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.dtr = snapshot_dtr,
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.map = snapshot_map,
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.end_io = snapshot_end_io,
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.resume = snapshot_resume,
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.status = snapshot_status,
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};
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@ -1306,11 +1383,18 @@ static int __init dm_snapshot_init(void)
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goto bad4;
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}
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tracked_chunk_cache = KMEM_CACHE(dm_snap_tracked_chunk, 0);
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if (!tracked_chunk_cache) {
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DMERR("Couldn't create cache to track chunks in use.");
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r = -ENOMEM;
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goto bad5;
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}
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pending_pool = mempool_create_slab_pool(128, pending_cache);
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if (!pending_pool) {
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DMERR("Couldn't create pending pool.");
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r = -ENOMEM;
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goto bad5;
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goto bad_pending_pool;
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}
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ksnapd = create_singlethread_workqueue("ksnapd");
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@ -1324,6 +1408,8 @@ static int __init dm_snapshot_init(void)
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bad6:
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mempool_destroy(pending_pool);
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bad_pending_pool:
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kmem_cache_destroy(tracked_chunk_cache);
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bad5:
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kmem_cache_destroy(pending_cache);
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bad4:
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@ -1355,6 +1441,7 @@ static void __exit dm_snapshot_exit(void)
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mempool_destroy(pending_pool);
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kmem_cache_destroy(pending_cache);
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kmem_cache_destroy(exception_cache);
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kmem_cache_destroy(tracked_chunk_cache);
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}
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/* Module hooks */
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@ -130,6 +130,10 @@ struct exception_store {
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void *context;
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};
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#define DM_TRACKED_CHUNK_HASH_SIZE 16
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#define DM_TRACKED_CHUNK_HASH(x) ((unsigned long)(x) & \
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(DM_TRACKED_CHUNK_HASH_SIZE - 1))
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struct dm_snapshot {
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struct rw_semaphore lock;
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struct dm_target *ti;
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@ -174,6 +178,11 @@ struct dm_snapshot {
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/* Queue of snapshot writes for ksnapd to flush */
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struct bio_list queued_bios;
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struct work_struct queued_bios_work;
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/* Chunks with outstanding reads */
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mempool_t *tracked_chunk_pool;
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spinlock_t tracked_chunk_lock;
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struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
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};
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/*
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